- var_dump: documentation ( source)
<?php
$a = new DateTime('2020-01-01 23:59:40');
$b = new DateTimeImmutable('2020-01-01 23:59:40');
var_dump($a, $b);
$a->add(new DateInterval('P1D'));
$c = $b->add(new DateInterval('P1D'));
DateTimeImmutable::fromMutable($a);
var_dump($a, $b, $c);